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Discussion Starter #1 (Edited)
Hoping somebody much smarter than me can help me out here. These are some measurements of my 10 siht18's 4cf sealed. The no audyssey(no eq) measurement was taken a different day and at a different volume level but I think the other three I kept the mv the same for all. Those three are post audyssey with extra eq via minidsp. I went sealed because I had the space and budget to go multiple sealed and have never experienced single digit extension and I wanted to try it out. These are d4's powered by 3 inuke 6000's, 2 per channel at 4ohms for what I think is around 1100 watts per sub. I'm measuring with a omnimic v2 mic with calibration file which is supposed to measure down to 5 hz. The room is 14x15x9 with an open stairway to the upstairs. It looks like my output starts dropping at 12 hz and drops fast after 10. Is this the inuke's roll off? Other equipment is Onkyo txnr3007>Minidsp>inukes. I can bring it up some but the same general profile remains below 10hz. I had an idea and played around with the rew eq tab and simmed up some responses that get me flat to 5-6hz by pulling down everything above 12hz down to a couple db higher than the 6hz level. Then I thought I could just bring the whole response back up with the amp gains. Haven't tried it yet in reality only with the sim. Is this a horrible idea? I only know enough to be somewhat hazardous to my gear so I need some help. If I do this will I just be reducing my overall subwoofer headroom by whatever amount of db gain I add back? Even if all the eq cuts bring the entire response down by 10-12db then I add back 10-12db in amp gain. Would I be back at square one with the same headroom or will I lose it? Any other reasons this is a bad idea or is it a try it out and see what happens thing (which I will anyway)? Even with the huge boosts applied on the brown line I still wasn't clipping the amps with the incredible hulk end fight at -5 on the mv. I never watch higher than -12 in my room, its just too loud for me except for demos. Sorry for the long unorganized read of a post and I sure hope some smart folks made it all the way through, If theres anything I left out that will make it easier to help me with this please let me know.

Thank You in advance for any help at all,
Wiles
 

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I am no Jedi, but may be able to give you some ideas.


Start by close micing 1 speaker with the rest off to get the room out of the equation. I'm guessing from the couple things I've read about single digit room gain that you should have a fairly steady rise in response, but it is a variable.


It looks like you have some steep roll off from equipment at 9hz. But it may be the room.
It may be the inuke doing a lot of that. The charts I've seen have it taking a nosedive between 10hz and 5hz.
Looks like your avr is rated at -3db at 5hz...what it actually does, no clue.
I think the minidsp is pretty flat to very low.


All the roll offs will add up to give you a lot of roll off between 2.5hz and 10hz (2 octaves in 7.5hz)


The thing I can't quite grasp is that all 3 lines are the same at 7hz regardless of what you do to the EQ.


It looks like you can't bottom out the drivers with that amp and box size. I do think you are risking cooking the coils, but if you're not worried about that... You should be able to add a 5hz peq boost to counteract the roll off and keep adding gain to the peq till the amp clips. Maybe +9 or +12 with a Q of 2. Work your way up 1db at a time, take a rew sweep, and overlay them.
 

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Discussion Starter #3
I am no Jedi, but may be able to give you some ideas.


Start by close micing 1 speaker with the rest off to get the room out of the equation. I'm guessing from the couple things I've read about single digit room gain that you should have a fairly steady rise in response, but it is a variable.


It looks like you have some steep roll off from equipment at 9hz. But it may be the room.
It may be the inuke doing a lot of that. The charts I've seen have it taking a nosedive between 10hz and 5hz.
Looks like your avr is rated at -3db at 5hz...what it actually does, no clue.
I think the minidsp is pretty flat to very low.


All the roll offs will add up to give you a lot of roll off between 2.5hz and 10hz (2 octaves in 7.5hz)


The thing I can't quite grasp is that all 3 lines are the same at 7hz regardless of what you do to the EQ.


It looks like you can't bottom out the drivers with that amp and box size. I do think you are risking cooking the coils, but if you're not worried about that... You should be able to add a 5hz peq boost to counteract the roll off and keep adding gain to the peq till the amp clips. Maybe +9 or +12 with a Q of 2. Work your way up 1db at a time, take a rew sweep, and overlay them.
Thanks More. I have a nearfield measurement I will post up this evening after work and see if that adds anything to the equation. I can't eq any lower than 10hz with the minidsp. It seemed like no matter how much boost I added to a 10hz low shelf I still had the same general response below 10hz except it would all come up some. I thought of something earlier today and I'm not sure about it but I was thinking if I cut everything above 7hz or so to equal my output at 7hz then wouldn't my total sub max output be limited to whatever I can do at 7hz? That would probably be pretty underwhelming overall. I will keep playing around with it and hopefully get some more input around here.
 

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Thanks More. I have a nearfield measurement I will post up this evening after work and see if that adds anything to the equation. I can't eq any lower than 10hz with the minidsp. It seemed like no matter how much boost I added to a 10hz low shelf I still had the same general response below 10hz except it would all come up some. I thought of something earlier today and I'm not sure about it but I was thinking if I cut everything above 7hz or so to equal my output at 7hz then wouldn't my total sub max output be limited to whatever I can do at 7hz? That would probably be pretty underwhelming overall. I will keep playing around with it and hopefully get some more input around here.
I'm pretty sure you can eq lower than 10hz with minidsp, but you need to manually input the values. Biquad values from rew or something like that. I don't have one but you can read up on it. Again, I wouldn't send that much power to these subs. But people seem to do it without letting the smoke out. I would shut off 8 of them and just mess with one channel to limit catastrophic failure. Or wire one to 8ohm and just mess with one sub.


Cutting everything above 10hz and rising the master gain should get you the same result as boosting under 10hz.


There is/was a problem with some
 

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He has an 18db difference between 7hz and 12hz though. And eq at 10hz doesn't change 7hz. I think your red line is a little too straight, should start heading way downward by 5hz.




From above:
"I'm measuring with a omnimic v2 mic with calibration file which is supposed to measure down to 5 hz."


Is it the mic? A room mode in his tiny 14x15 room? I would expect room gain to leave anything under 10hz flat with sealed boxes.
 

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"I think your red line is a little too straight, should start heading way downward by 5hz."


that is the measured response of a first order high pass at 7hz (down 4.7db at 5hz). the different scales can trick the eye (which is why I translated it to his measurement).
 

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Discussion Starter #11 (Edited)
Ltd I'm using a omnimic v2 mic with supplied calibration file. It's a usb mic so there is no soundcard. My laptop has hdmi out and I'm using asio4all with rew. Attached is a nearfield measurement I took outdoors with the mic a few inches from the dustcap and the sub about 2.5 ft off the ground.

I haven't read about the minidsp doing below 10hz. Can you point me to where that was discussed?

Just checked my minidsp software and if i put in any number below 10 it will revert back to 10 as soon as I hit enter.
 

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"The room is 14x15x9 with an open stairway to the upstairs."


the close mic response shows that the subs are rolling just a hair faster what one would expect from the driver/enclosure/amp, so that's probably not the problem.


after quite a bit of time thinking about this one, i wonder if the suckout around 8 hz is coming from the open stairway to the upstairs acting as some sort of extremely large tuned resonant bass trap. i'm not even sure if that is possible.


that suckout is not present in the close mic measurement and appears to be good for about 10db or so of missing spl.
 

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when i enter the size of your room as an "enclosure" and then guesstimate the approximate dimension of your stairway, i end up with something that looks like this:





that is a fairly high q resonance. the inverse of that doesn't look too different from what you are measuring.


who knows...
 

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Sweep each of the 10 SI's individually from the LP and post the chart of those 10 sweeps.

That will give more insight into which subs might be misperforming.

That graph looks like 50% of your subs are out of phase, but audyssey was able to correct it, so it can't be a complex phase problem.

Don't worry about the
 

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Discussion Starter #16 (Edited)
Ltd, sounds like I'm s.o.l. for much below 10hz then. Bummer. Btw how do you get your attachments to be big and not just thumbnails?

BTH, I've attached some measurements I had of the front middle 2 subs, front corner subs, rear sub and combined response. I can take out the huge boost at 40 no prob or audyssey gets rid of it too. I've let audyssey do it and I've done it manually before running audyssey and can tell no difference audibly. I will measure all individually if you think that will be beneficial. It will be a couple days before I can do it though. I just figured that big hump was a combination of my room and ten sealed subs with a resonant frequency around 40. The nearfield is humped in the same area too so I thought it was just the nature of the beast. What is it your seeing that makes you think I have a phaseissue? Suppose I could wired a driver backwards at some point. The front corners are dual opposed boxes, front middle has 2 single enclosures and one dual opposed in the rear corner with 2 singles stacked on it.

I appreciate the input, thank you. Keep the thoughts coming too, I gotta get this figured out. It does sound great though I just want what its capable of.
 

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do you have a way to wall off the opening or close a door at the top of the stairs or something as a way of testing this theory?


to insert a picture, go to advanced editor mode so you can see the attachments button.


launch the edit attachments to get the window that lists your attachments.


click on the one that you want to insert "big".


it will launch it in its own window.


copy the url from that window.


go back to the editor window where you want to insert the image and click on the insert image icon (the one with the triangles/mountains in it).


paste in the link.
 

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Discussion Starter #18
Thanks Ltd but that's more info than my hungover brain can process atm. I'll read that one again later. I don't have a door there or a big enough piece of wood. Would a half sheet of mdf work? Just cover the bottom half maybe?
 

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if you block off or partially block off the stairway and measure a difference then you may be onto something.




it might be interesting to run a couple of sweeps with the mike at a couple places along the stairs to see if the resonant peak shows up there.
there energy has to be going somewhere.
 

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Discussion Starter #20
if you block off or partially block off the stairway and measure a difference then you may be onto something.




it might be interesting to run a couple of sweeps with the mike at a couple places along the stairs to see if the resonant peak shows up there.
there energy has to be going somewhere.
I will measure on the stairs. Probably not until monday but maybe tomorrow. What exactly should I be looking for with those measurements?
 
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